Belgian unit checked for cracks

08 August 2012

Unit 3 of the Doel nuclear power plant in Belgium is to remain offline while investigations are made into possible cracks in its reactor pressure vessel. As a precaution, other Belgian reactors will also be checked for cracks, the national regulator said.

Plant operator Electrabel took the 1006 MWe pressurized water reactor offline on 2 June for a scheduled maintenance and a mandatory ten-year safety inspection. During these inspections, the reactor pressure vessel was examined using a new kind of ultrasonic sensor. The utility informed the Belgian nuclear regulator, the Federal Agency for Nuclear Control (FANC), that these results indicated the possible presence of cracks in the vessel.

Electrabel intends to conduct additional examinations using a different type of ultrasonic sensor, which has given reliable results in the past. However, analysis of the second set of results will take some time, the utility noted.

An Electrabel spokeswoman told World Nuclear News that the second ultrasonic examination of Doel 3's pressure vessel could indicate that the new examination technology has simply given false results.

The regulator has ruled that Doel 3, which began operating in 1982, must remain idle until the results of the additional examination of its pressure vessel have been analysed. The reactor will remain offline until at least the end of the month, it said.

FANC said that unit 2 at the Tihange plant is due to be shut down next month for similar safety inspections, including an ultrasonic examination of its pressure vessel. The regulator noted that the pressure vessel for Tihange 2 was forged in the 1970s by Rotterdam Drydock Company, the same supplier for Doel 3. Results of ultrasonic scans on Tihange 2's vessel are expected by the end of September.

A ten-year licence extension for Tihange unit 1 was recently approved by the regulator. While that reactor's pressure vessel was supplied by Cockerill Seraing, FANC has requested that an ultrasonic examination be conducted in 2013. The vessels for the newer Doel 4 and Tihange 3, which were manufactured by Japan Steel Works, will eventually undergo similar inspections, it said.

FANC said that any decision to allow Doel 3 to restart operations will be based on a safety assessment of the complete results and on the advice of its scientific council, and will be subject to an international audit.

The incident has provisionally been rated as Level 1 on the International Nuclear Event Scale (INES). However, FANC said that this rating may be reassessed when more information and the results of the new analysis are available.